Have you check the compression of each cylinder? That's the first step when internal problems are suspected. A low reading will point to the cylinder or cylinders that likely have a problem and suggest where to look when you remove the head and the blown gasket. I couldn't see much in the video, but with the head off it will be easy to assess the block's condition and then judge if there's damage or if what the scope showed was mostly just wear and tear. I bet the block will be in better shape than you fear. However, expect to replace the head. They crack easily, especially those with jet-valves.